Chapter 3:Chapter 3:Life Cycles and Life Cycles and

Biological ChangeBiological ChangeLesson 13Lesson 13

Causes of ExtinctionCauses of Extinction

SourceSource

TCAP CoachTCAP Coach 55thth grade grade ScienceScience

ObjectiveObjective

The student will compare the causes The student will compare the causes that led to the extinction of various that led to the extinction of various organisms.organisms.

Cause of ExtinctionCause of Extinction

When the habitat that an organism is When the habitat that an organism is adapted to changes or disappears, adapted to changes or disappears, fewer of these organisms survive.fewer of these organisms survive.

When fewer organisms survive, there When fewer organisms survive, there are fewer left to reproduce.are fewer left to reproduce.

Over time, the population gets Over time, the population gets smaller and smaller.smaller and smaller.

Eventually, the species will become Eventually, the species will become extinct.extinct.

Cause of ExtinctionCause of Extinction

In this lesson, you will learn about In this lesson, you will learn about the causes of extinction.the causes of extinction.

Habitat DestructionHabitat Destruction

Plants and animals thrive in certain Plants and animals thrive in certain habitats. When their natural habitat habitats. When their natural habitat shrinks, fewer members of a shrinks, fewer members of a population can thrive.population can thrive.

Humans have changed much of the Humans have changed much of the surface of the Earth.surface of the Earth.

Habitat DestructionHabitat Destruction

We use land for our houses and for We use land for our houses and for growing crops. Whenever an acre of growing crops. Whenever an acre of land is changed from a natural land is changed from a natural habitat, such as a forest, to cleared habitat, such as a forest, to cleared land for human use, habitats become land for human use, habitats become smaller.smaller.

The animals that were living in the The animals that were living in the original forest must find a new original forest must find a new habitat to live in. habitat to live in.

Habitat DestructionHabitat Destruction

When much of an When much of an animal’s habitat is animal’s habitat is destroyed, it is destroyed, it is harder for that harder for that species to survive.species to survive.

Habitat DestructionHabitat Destruction

Even when some original habitat is left, Even when some original habitat is left, this habitat is often broken into smaller, this habitat is often broken into smaller, isolated pieces. Human activity can also isolated pieces. Human activity can also pollute a natural habitat. People often pollute a natural habitat. People often use fertilizers and insecticides on crops use fertilizers and insecticides on crops and recreational areas. These chemicals and recreational areas. These chemicals move into animals’ habitats and can move into animals’ habitats and can affect their life cycles. Many amphibian affect their life cycles. Many amphibian species are endangered because of species are endangered because of pollution of the environment.pollution of the environment.

Habitat DestructionHabitat Destruction

Habitat DestructionHabitat Destruction

Other species become endangered Other species become endangered when new species move into their when new species move into their habitat. Many of these new alien habitat. Many of these new alien species are introduced by humans. species are introduced by humans.

The new species can compete for The new species can compete for food and space and put stress on food and space and put stress on native populations. native populations.

These new species often have few or These new species often have few or no natural predators.no natural predators.

Over-huntingOver-hunting

Over the last 200 years, many animals Over the last 200 years, many animals have become extinct because of over-have become extinct because of over-hunting. One example is the passenger hunting. One example is the passenger pigeon.pigeon.

Over-huntingOver-hunting

As Europeans began to settle the United As Europeans began to settle the United States, they hunted passenger pigeons States, they hunted passenger pigeons to eat and for sport. It is believed that to eat and for sport. It is believed that the original population of passenger the original population of passenger pigeons was well over a billion.pigeons was well over a billion.

But by 1914, the species was extinct. But by 1914, the species was extinct. Other bird species became extinct after Other bird species became extinct after they were hunted for their beautiful they were hunted for their beautiful plumes.plumes.

Over-huntingOver-hunting Other species have been hunted to near Other species have been hunted to near

extinction. The American bison was close to extinction. The American bison was close to extinction for many years but has begun to extinction for many years but has begun to make a recovery. This is because widespread make a recovery. This is because widespread hunting of bison has stopped and some of their hunting of bison has stopped and some of their habitat has been restored.habitat has been restored.

Mass ExtinctionsMass Extinctions

Throughout Earth’s history, there have Throughout Earth’s history, there have been a few periods of mass extinctions.been a few periods of mass extinctions.

A mass extinction occurs when many A mass extinction occurs when many species go extinct at the same time.species go extinct at the same time.

Mass extinctions may be caused by Mass extinctions may be caused by climate change. As the climate changes climate change. As the climate changes all over Earth, habitats all over Earth are all over Earth, habitats all over Earth are changed and destroyed.changed and destroyed.

Mass ExtinctionsMass Extinctions

A mass extinction happened when the A mass extinction happened when the dinosaurs became extinct. Many scientist dinosaurs became extinct. Many scientist believe that this mass extinction was caused believe that this mass extinction was caused by a meteor striking Earth. When the meteor by a meteor striking Earth. When the meteor struck Earth, huge amounts of dust blew into struck Earth, huge amounts of dust blew into the atmosphere. This dust blocked sunlight the atmosphere. This dust blocked sunlight and caused a cooling all over the Earth’s and caused a cooling all over the Earth’s surface. As plants began to die out, so did surface. As plants began to die out, so did animals that depended on the plants for food. animals that depended on the plants for food. Eventually the dinosaurs died out. Now we Eventually the dinosaurs died out. Now we only have fossil evidence of the dinosaurs.only have fossil evidence of the dinosaurs.

Mass ExtinctionsMass Extinctions

AdaptationsAdaptations

Not all species become extinct when their Not all species become extinct when their habitats change. habitats change.

Some species have characteristics that Some species have characteristics that can help them survive in a changing and can help them survive in a changing and changed habitat.changed habitat.

Over time, these characteristics can help Over time, these characteristics can help them thrive in a new environment. them thrive in a new environment.

Small mammals living alongside the Small mammals living alongside the dinosaurs thrived after the dinosaurs dinosaurs thrived after the dinosaurs became extinct. became extinct.

Extinct AnimalsExtinct Animals

Extinct AnimalsExtinct Animals

Which term describes Which term describes what happens when what happens when

many species go extinct many species go extinct at the same time?at the same time?

A. Over-huntingA. Over-hunting B. Mass extinctionB. Mass extinction C. Climate changeC. Climate change D. metamorphosisD. metamorphosis

Which term describes Which term describes what happens when what happens when

many species go extinct many species go extinct at the same time?at the same time?

B. Mass extinctionB. Mass extinction

What do scientist think What do scientist think is the main cause of is the main cause of mass extinctions?mass extinctions?

A. Over-huntingA. Over-hunting B. PollutionB. Pollution C. Climate changeC. Climate change D. Habitat fragmentationD. Habitat fragmentation

What do scientist think What do scientist think is the main cause of is the main cause of mass extinctions?mass extinctions?

C. Climate changeC. Climate change

Which of these helps an Which of these helps an organism thrive in organism thrive in changing habitats?changing habitats?

A. PollutionA. Pollution B. Habitat destructionB. Habitat destruction C. AdaptationC. Adaptation D. Climate changeD. Climate change

Which of these helps an Which of these helps an organism thrive in organism thrive in changing habitats?changing habitats?

C. AdaptationC. Adaptation